Electromagnetic transmission performance of carbon fiber

What is Electromagnetic waves?

Electromagnetic waves have gradually become the fourth largest environmental pollution in addition to water, air, and noise. In addition, the electronic, electrical and communication equipment manufactured by people will also produce electromagnetic radiation, and the development and research of electromagnetic shielding materials has gradually become an issue of increasing concern. Carbon fiber has good electromagnetic shielding performance, and carbon fiber has excellent electrical and thermal conductivity, good flame retardancy, very low thermal expansion coefficient, low radiation absorption and a series of advantages.

Electromagnetic shielding is the use of conductive or magnetic materials to limit electromagnetic radiation within a specified space. 

There are generally two purposes of electromagnetic shielding, to limit internal radiated electromagnetic energy from leaking out of the internal area, or to prevent external radiation interference from entering a certain area. According to the shielding principle, electromagnetic shielding can be divided into three types: electric field shielding, magnetic field shielding and electromagnetic field shielding. The essence is to study how electromagnetic fields are distributed in various specific problems.

Electromagnetic shielding comparison chart

There are many ways to classify electromagnetic shielding materials

mainly including ferromagnetic materials and metal good conductor materials, surface conductive shielding materials and filled shielding composite materials. Among them, the filled shielding composite material is an electromagnetic shielding material product composed of a matrix with good electrical insulation, conductive fillers with excellent conductivity and other additives, and carbon fiber belongs to this electromagnetic shielding material. Under the harsh conditions of 60℃ and 90% relative humidity, after 2000h durability test, the carbon fiber shielding material made of carbon fiber with a length of 3mm and CF/PVC resin with a content of 5wt% can achieve a shielding effect of more than 30dB. The CF content is 10wt%hi, which can achieve a shielding effect close to that of copper foil.

The main reason that carbon fiber has electromagnetic shielding ability is because of its good electrical conductivity. The common volume resistivity of carbon fiber is between (0.8~1.8)×10-3Ω·cm, and the conductivity will increase with the increase of heat treatment temperature. Therefore, after high-temperature graphitization treatment, carbon fiber can become an excellent reflective material for electromagnetic waves. At present, the research on carbon fiber by state-owned enterprises mainly focuses on the mechanical properties, and there is still relatively little research in the electromagnetic field.

Carbon fiber electromagnetic shielding end cap

When the arrangement direction of the carbon fiber is parallel to the incident electric field, since the carbon fiber itself is a kind of electrical loss material with excellent conductivity, a large conduction current will be generated in the carbon fiber at this time, and the incident electric field will be strongly reflected, which is close to The reflection effect of metal; the other case is when the arrangement direction of carbon fiber is perpendicular to the incident electric field, the carbon fiber acts as the loss medium of the radar wave at this time; and when the angle between the arrangement direction of the carbon fiber and the incident electric field is uncertain, Since the reflected electric field is not parallel to the incident electric field, the reflected electric field will produce a reflected electric field component perpendicular to the incident electric field, which has a certain wave-eliminating effect.

The advantages of carbon fiber that as a electromagnetic shielding material

In addition to excellent electromagnetic shielding performance, carbon fiber also has the characteristics of high strength and light weight. In foreign countries, carbon fiber composite materials have been applied to stealth aircraft and other aircraft, and the carbon fiber has been modified to reduce electromagnetic wave reflection. In China, carbon fiber electromagnetic shielding technology is relatively not as mature as abroad. The main research areas of most companies focus on resin-based composite materials with carbon fiber as filler. The development and research of carbon fiber electromagnetic shielding performance is still a long way to go.